This invention relates to a vehicle for transporting loads and, more particularly, to an improved article storage and retrieval storage rack entry vehicle capable of detecting the proximity of loads to the vehicle.
A variety of systems have been employed in the past for the storage and retrieval of articles in high volume warehouses. One such system comprises a plurality of storage racks separated from each other by aisles. The disadvantage of such a system is that the density of storage for a storage space of given cubic volume is reduced because of the large number of aisles that must be provided for the operation of a storage and retrieval vehicle.
In order to minimize this loss of storage density, various high density storage systems have been devised in which the number of aisles per cubic volume of storage space has been substantially reduced and replaced by storage structures. In one such horizontal bin system, a rack entry vehicle is employed which moves into elongate bins in the rack to either store an article in a bin at a designated location or to retrieve a designated article from a bin. It is this latter form of high density storage system with which the present invention is concerned.
Rack entry vehicles in such high density systems are subject to several potential problems. For example, the loads which such vehicles must handle are frequently of substantial weight, sometimes as much as 2-3 tons. Even though the loads handled by the rack entry vehicles are frequently palletized, the loads still may be distributed unevenly. Compounding this problem is the fact that the storage racks in such systems are frequently many stories in height and are of substantial length and width. In such an environment, it is important for the vehicle to accurately detect its proximity to the palletized loads. If a load is not properly positioned on the vehicle, or if the vehicle rams a load resting on the rack, the load could tumble through the rack structure, thereby damaging other loads or causing them to fall.
Devices for determining the presence of a palletized load above a rack entry vehicle have been developed in the past. One such system is shown in U.S. Pat. No. 3,973,685 (Loomer--Aug. 10, 1976.) Loomer uses a visible light transmitter which projects a continuous light beam along a first axis and a visible light receiver which receives a reflected light beam along a second axis. The transmitter and receiver are angularly-oriented to enable the first and second axes to intersect at a junction located in the plane of the pallet to be sensed. Experience has shown that the Loomer system has defects which limit its usefulness. For example, the Loomer receiver is subject to errors because of its sensitivity to ambient light. It is also subject to errors in the event that a relatively small target is sensed. Since the light beam axes intersect in only one plane, it is possible for the vehicle to pass through that plane before the receiver can detect the presence of the target.
The applicant has discovered that a load proximity detector diametrically opposed to the device described by Loomer improves the accuracy and reliability with which the position of loads can be detected. A preferred form of the present invention includes a radiation source which projects optical radiation along a first axis and a detector for receiving optical radiation along a second axis. The first and second axes are parallel, and this feature enables radiation to be received continuously from a pallet or load as soon as the receiver is within a predetermined range. The range is adjustable by varying the intensity of the radiation, the sensitivity of the detector, or the angle at which the radiation strikes the object being detected. As used in this specification and these claims, optical radiation means electromagnetic radiation within the infrared, visible and ultraviolet bands of the spectrum from about 10.sup.-3 to about 10.sup.-8 meters in wavelength.
According to other aspects of the present invention, the radiation lies within the infrared portion of the electromagnetic spectrum, and the transmitter is pulsed or cycled. These features make the invention immune from ambient light conditions. By use of the foregoing features, small loads or pallets can be detected with a degree of accuracy and reliability previously unattainable.
These and other features and advantages of the present invention will be more clearly understood through a consideration of the following detailed description.